Femtosecond optical frequency combs have led to a revolution in optical metrology, spectroscopy and frequency standards by providing a precise ruler to measure optical frequencies. An optical frequency comb consists of a mode-locked femtosecond laser that is actively stabilized to generate a stable optical pulse train. The optical spectrum of the resultant laser output consists of tens of thousands of equally spaced narrow linewidth “comb-teeth”, with typical spacing between each teeth of 0.1-1 GHz. The absolute frequency and linewidth of each tooth is determined by two parameters: the laser cavity length, which determines the spacing between the teeth, and the carrier-envelope phase offset frequency (fceo), which determines the absolute frequency of the central comb tooth. High speed control of both of these parameters is important to reduce the linewidth of each comb tooth and minimize the error in optical frequency determination.